1. Field of the Invention
The present invention relates to a liquid container to accommodate a variety of kinds of liquids, such as printing inks and liquids specially designed to improve ink fixing performance. Such a liquid container may include an ink tank detachably mounted in an ink jet printing apparatus.
2. Description of the Related Art
An ink jet printing apparatus prints an image on a print medium by supplying ink from an ink tank to a print head and ejecting ink from the print head. A so-called serial type ink jet printing apparatus has a carriage mountable a print head and performs printing by ejecting ink onto a print medium from ejection nozzles of the print head mounted on the carriage as the carriage is moved relative to the print medium. A so-called full-line type ink jet printing apparatus uses a print head having ejection nozzles arrayed over a range matching a width of a print medium. The full-line type performs printing by ejecting ink from the ejection nozzles of the print head toward the print medium fed under the print head.
An ink tank for supplying ink to these print heads holds the ink at a predetermined negative pressure. The negative pressure is intended to create a force to hold a meniscus of ink formed in every ejection nozzle of the print head and thereby prevent a possible leakage of ink from the ejection nozzles. The negative pressure is set in an appropriate pressure range that assures an ink ejection operation of the print head.
Among a mechanism for creating such a negative pressure is known a construction in which a porous member such as sponge to soak and hold ink is installed in the ink tank to create an appropriate negative pressure in the tank by an ink holding force generated by the porous member. There is also known a construction in which a bag member, formed of an elastic material such as rubber that produces a tension in a direction that expands its volume, is filled with an ink to apply a negative pressure to the ink by the tension the bag member has produced.
Also known is a construction in which a bag member formed of a flexible film is attached with a spring inside or out-side it to bias the film in a direction that expands the volume of the bag member, thus applying a negative pressure to the ink contained in the bag member. Among the ink tank using this negative pressure mechanism are those described in Japanese Patent Laid-Open No. 2007-069351 and U.S. Pat. No. 6,168,267.
Japanese Patent Laid-Open No. 2007-069351 and U.S. Pat. No. 6,168,267 describe ink tanks 100 constructed as shown in FIG. 22A and FIG. 22B. A case 101 formed with an ink supply port (not shown) is attached with a flexible convex film 102 to form an ink accommodation space 103, in which a spring 104 is installed to generate a negative pressure. A plate member 105 is placed between the film 102 and the spring 104. The case 101 is attached with a cover member 106 that is formed with ribs 106A to restrict the movement of the plate member 105. In the ink tank 100 constructed of the film 102 and the spring 104, the plate member 105 is installed between them to transmit a pressure of the spring 104 to the film 102. The spring 104 and the plate member 105 are secured together by fastening or fusing to prevent positional shift.
The case 101 is preferably formed of the same resin material as the film 102. The ink accommodation space 103 formed by fusing them together is hermetically enclosed except for the supply port. An opening of the supply port is constructed to form therein by the negative pressure created by the spring 104 an ink meniscus of a size that prevents external air from getting into the ink accommodation space 103. For example, a mesh filter for generating an ink meniscus force may be fixed to the supply port.
The ink tank 100 having the ink accommodation space 103 formed of the film 102 as described above has an excellent ink accommodation efficiency, compared with an ink tank that generates a negative pressure as by a sponge soaked with ink.
Japanese Patent Laid-Open No. 2007-069351 also describes a method of forming the film 102 into a convex shape. This method involves first fusing a flat sheet material (a material to be formed into the film 102) to the case 101 of the ink tank and then forming the sheet material into a convex shape. That is, the flat sheet material is directly fused to the case 101 that is used as a forming die for the film 102. More specifically, by heating the sheet material fused to the case 101 and drawing air from between the sheet material and the case 101 by suction, the sheet material is formed into a convex shape conforming to the inner concave surface of the case 101. This obviates a troublesome step of positioning the convex-formed film 102 on the case 101 and allows the sheet material to be formed easily into the convex film 102 conforming to the shape of the case 101. Further, since the film 102, which is relatively difficult to handle, and the case 111 are constructed as one piece, they can be handled easily.
The ink tank 100 with the above negative pressure generation mechanism, when it falls in a direction crossing an expansion and compression direction of the spring 104 (in the direction of arrow in FIG. 22A), the plate member 105 may strongly impact the cover member 106, as shown in FIG. 22B. Since the film 102 between the plate member 105 and the cover member 106 is very thin, about 10-100 μmm thick, it is likely to be damaged by being pinched between them when it falls.
How the film 102 is damaged as a result of fall will be explained by referring to FIG. 22A and FIG. 22B.
The ink tank 100 falls in the direction of arrow crossing the expansion and compression direction of the spring 104 while maintaining the state of FIG. 22A in which it has been before the fall. Then, the instant the ink tank 100 hits the ground, ink contained in the ink tank 100 moves by its inertia in the direction of gravity. At this time, since the impacted part (lower part) of the ink tank 100 is the rigid case 101, the ink rushes to the impacted side of the ink tank 100 and at the same time moves in a direction that the film 102 can be deformed (in the direction of arrow in FIG. 22B). The plate member 105 similarly moves toward the impacted side by the inertia while at the same time a part of the plate member 105 on the impacted side is pushed in the direction of arrow of FIG. 22B by the ink moving toward the film 102 side. As a result, the part of the plate member 105 on the impacted side strikes against the inner surface of the cover member 106. Since this series of motions occurs instantaneously with high energy as the falling ink tank 100 hits the ground, the plate member 105 and the cover member 106 strike each other with force. This strong collision may result in the film 102 interposed between the plate member 105 and the cover member 106 being pinched between them and damaged.
Portions of the convex film 102 that are likely to be damaged are found to be, in particular, those portions 102A corresponding to corner portions 105A of the plate member 105 as shown in FIG. 23. FIG. 23 is a side view of the case 101 with the cover member 106 removed, as seen from the direction of arrow XXIII of FIG. 22A. As described in Japanese Patent Laid-Open No. 2007-069351 and U.S. Pat. No. 6,168,267, the plate member 105 often has a nearly rectangular shape as shown in FIG. 23. At the instant of collision between the roughly rectangular plate member 105 and the cover member 106, the plate member 105 is tilted to project the corner portions 105A causing them to come into point contact with the cover member 106. With stresses concentrated at the point contact portions, the film 102 may be broken at the portions 102A corresponding to the corner portions 105A.
To prevent the film 102 from being damaged easily, Japanese Patent Laid-Open No. H6-226993(1994) proposes a measure that mounts a guard member (shock absorbing material) to the plate member 105 and Japanese Patent Laid-Open No. S60-151055(1985) proposes a measure that places a shock absorbing material between the cover member 106 and the film 102.
In these measures, however, since an impact is absorbed by the shock absorbing material being deflected, to absorb a high energy produced by the impact of the falling ink tank requires increasing the thickness of the shock absorbing material to set the deflection range large. But setting the thickness of the shock absorbing material large limits a range in which the plate member is allowed to move, reducing the ink accommodation space, which in turn is likely to reduce the amount of ink that can be filled into the accommodation space. Another problem is that the shock absorbing material that is thin and still able to absorb shocks is limited to special materials such as silicone gel-like materials. Generally, a material with such a high energy absorbing capability is very expensive and may lead to a substantial increase in cost of the ink tank.
As shown in Japanese Patent Laid-Open No. 2007-069351, when a flat sheet material is formed into a convex film 102 by using a concave die member such as the case 101, the sheet material progressively cools and solidifies as it engages the concave die member. The sheet material finally contacts the bottom surface of the concave die member. The portion of the sheet material that contacts the bottom surface of the concave die member corresponds to the corner portions of the convex film 102. Therefore the corner portions of the film 102 are most stretched and become thin during forming. The corner portions of the film 102 are the portions 102A that also correspond to the corner portions 105A of the plate member 105. This means that the portions 102A of the film 102 are the most easily breakable portions.
When the case 101 is used as a forming die for the film 102, as in the case of Japanese Patent Laid-Open No. 2007-069351, the elongation and thickness of the sheet material depends on the depth of the recessed portion of the case 101. Japanese Patent Laid-Open No. 2007-062337 describes a method of forming the film 102 into a convex shape by using a die that folds the sheet material at half the depth of the recessed portion of the case 101. With this method, a portion of the film 102 at or around the folded part may be elongated so that it can be used as a convex film about two times as high as the depth of the recessed portion of the case 101. This keeps the elongation during forming of the sheet material to as little extent as possible, minimizing the partially thinned portion of the film 102. As a result, the film 102 can be protected against damage.
If an ink tank product with twice the current ink accommodation volume is planned, the ink tank size needs to be increased. To make the ink tank usable in a printing apparatus which is formed compact by reducing its height, it is difficult to increase the height and depth of the ink tank and the only option available is to change the width of the ink tank. The width of the ink tank is in the direction of depth of the case (equivalent to the lateral width of the tank in FIG. 22A), so the recessed portion of the case needs to have nearly two times the current depth. In the convex film forming method disclosed in Japanese Patent Laid-Open Nos. 2007-069351 and 2007-062337, as described above, the elongation and thickness of the sheet material changes with the depth of the recessed portion of the case. The deeper the recessed portion, the thinner the sheet material becomes. Further, since the increased ink tank capacity results in an increase in its weight and therefore an impact at time of fall, which in turn increases a possibility of the film damage.
One possible countermeasure to cope with this problem may involve using the forming method of Japanese Patent Laid-Open No. 2007-062337 and increasing the thickness of a pre-formed sheet material to increase the overall thickness of the entire convex film. However, this approach, although it can make the easily damaged film portions thick, increases the thickness of other portions more than necessary and therefore a film rigidity. As a result, the film behavior is not smooth as the ink in the ink tank is consumed. This in turn raises possibilities of the negative pressure in the ink accommodation space abruptly changing and of the ink in the accommodation space failing to be consumed completely.
Further, Japanese Patent Laid-Open No. H9-123476(1997) discloses a construction in which corner portions of a plate member is rounded to protect possible damages of the film 102. Simply rounding the corner portions of the plate member, however, cannot deal with the characteristic thickness distribution of the convex film formed by a concave forming die, as described later. It is also necessary to reduce the size of the plate member, giving rise to a possibility of the ink accommodation efficiency reducing significantly.